SEMI-ACTIVE CONTROL OF VERTICAL VIBRATION OF SUSPENSION BRIDGES SUBJECTED TO EARTHQUAKE EXCITATIONS USING MR DAMPERS AND FUZZY LOGIC

In this paper, a semi-active control technique is presented to mitigate the seismic vertical response of suspension bridges using magneto-rheological (MR) dampers and fuzzy logic. Fuzzy logic is a kind of controller that can directly determine the input voltage of an MR damper from the responses of the structure, and MR dampers are semi-active control devices which MR uid is used in their structure. MR dampers have received signi- cant attention in recent years because they retain the reliability of passive control systems and the advantage of adjustable parameter characteristics of an active control system, simultaneously. The magneto rheological damper is an attractive candidate in semi-active control of structures because of its advantageous features including: no need for a major energy source and high power capacity, adjustable power, fast response, and safe operation in cases of power failure.
To achieve this goal, a large scale MR damper (2200 KN) is used, and the Vincent-Tomas suspension bridge, located in Los Angeles, USA, has been chosen for the numerical example. Installation of the dampers at degrees along the bridge span, far from the towers, should be highlighted as an extremely challenging problem in this study to increase damper eciency. In order to solve this problem, use of a rigid truss is proposed, and dierent schemes are also suggested to install MR dampers along the bridge span. The equation of motion of the system, using generalized modal coordinates, is written in the state-space form and the responses of the bridge are calculated under application of 15 major, world-wide earthquake accelerograms. Dierent inputs and rule bases are proposed for the fuzzy controller in this research. The characteristics of the fuzzy controller, and the number and position of the dampers are optimized by the trial and error method. Finally, three models with optimal position and number of dampers with optimal fuzzy control parameters are proposed.
A comparison between the uncontrolled and controlled responses indicates that the proposed semi-active control technique can eectively suppress the vertical responses of the example bridge.